This invention relates generally to the administration of bioactive substances to animals. More particularly, this invention relates to injectable compositions and methods for extended release of macromolecules such as growth hormones and growth hormone releasing factors in animals.
In recent years, major efforts have been made to discover cost-efficient ways to treat animals with growth hormones, growth hormone releasing factors and other bioactive substances over extended periods of time. The achievement of effective extended release (also commonly referred to as "sustained" or "prolonged" or "controlled" release) compositions and methods has been central in these efforts. These compositions and methods are designed to deliver effective amounts of bioactive substance over extended periods of time following administration. This reduces labor costs by reducing the number of administration procedures during an overall treatment regimen. Extended release of the substance also allows for treatment in situations where it would otherwise be impracticable, for instance during range feeding of animals raised for consumption. Further, effective extended release avoids large fluctuations in plasma levels of the bioactive substance, initially too high and then rapidly too low, which occur upon injection of standard, non-extended release formulations.
There has remained a need for improved injectable compositions and methods which provide extended release of growth hormone-related substances such as growth hormones and growth hormone releasing factors in animals. The compositions preferably are easily formulated using readily available materials, and the preferred preparative procedures should not be potentially damaging to the active materials.